This PR introduces a new keyboard shortcut to improve the efficiency of
selecting components in the app. Users can now quickly select components
using Meta + Shift + C for Mac and Ctrl + Shift + C for Other devices
(Windows/Linux)

    
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## Summary by cubic
Add a shortcut to quickly activate the component selector from the
preview. Use Meta+Shift+C on macOS and Ctrl+Shift+C on Windows/Linux.

- **New Features**
- Added useShortcut hook to handle key combos and prevent default on
match.
  - Wired shortcut in PreviewIframe with OS detection for Meta vs Ctrl.
- Forwarded keydown events from the iframe to the parent via postMessage
(dyad-shortcut-triggered) so the shortcut works inside preview content.

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